Ammunition casings, formed from hardened materials, generally stainless steel, have met many of the needs of modern warfare, while failing to meet others. The choice of stainless steel has yielded casings which have a great deal of strength and have been able to withstand the rigors of combat. However, at the same time, stainless steel, as a metal, has several disadvantages.
The main disadvantage of the use of stainless steel casings has been in the reaction of the encased ammunition to heating, including fires within ammunition storage areas. With a hardened shell having a melting point higher than the ignition temperature of the enclosed ammunition, stainless steel casings contain the expanding gases created during ammunition cook-off. When the pressure of the expanding gases is great enough, the casing ruptures explosively, generating explosion damage and metal fragments. In order to preclude a chain reaction of stored munitions, land-based ammunition dumps are typically divided into a series of bunkers separated by sufficient distance to isolate one bunker from another. This type of isolation is not available for shipboard ammunition storage due to the limited available space and due to the proximity of other flammable or explosive materials including fuels, oxygen, high voltage electrical circuits and the like.
Additionally, because of the hardened nature of the stainless steel casings, all machining must be performed after the initial molding of the casing. This means that the interior of a hollow cylindrical casing must be machined using special tools. This process is lengthy and slows the time of manufacture for casings. Finally, although hardened materials, such as stainless steel, provide high tensile strength, this strength comes at the cost of weight. The weight of the casing can affect the ease of transportation of the ammunition itself and the flight characteristics of encased missile weapons.
Numerous other prior art technologies have addressed the problems of munition cook-off on shipboard. For example, U.S. Pat. No. 4,991,513 describes a means for providing vent holes in munition casing using a twisting mechanism to open or close the holes (analogous to opening and closing a salt or pepper shaker). Each of these prior technologies has resulted in further disadvantages, increased weight, poor sealing of the casing, increased complexity requiring operator action to ready the munition, increased cost and other disadvantages. What is desired is a munition casing having increased strength, lower weight, less cost, while still retaining the insensitive characteristics when subjected to high temperatures or fire.